1. Field of the Invention
The present invention is broadly concerned with an improved, preferably prefabricated expansion joint assembly adapted for use in joining concrete roadway slabs in order to properly transfer vertical shearing forces while minimizing stress cracking of the slabs commonly experienced using conventional dowel-type expansion joints. More particularly, the invention pertains to an expansion joint assembly including pairs of elongated, obliquely oriented load transfer bars each configured to present a general X-configuration and bridging an expansion joint between concrete slabs, with the ends of the respective load transfer bars being embedded within the slabs; the oblique bars are preferably unconnected in the joint region, and structure may be provided for coupling the embedded bar ends within each slab to each other in order to safely accommodate expansion and contraction of the slabs while also insuring proper load transfer therebetween.
2. Description of the Prior Art
In the construction of concrete roadways, it is common practice to install expansion joint assemblies at spaced locations, so that the completed roadway can properly expand and contract under varying temperature and environmental conditions. Typically, such expansion joint assemblies make use of a plurality of laterally spaced apart dowel units including a tubular barrel embedded within one concrete slab, with a dowel aligned with the barrel and embedded in the adjacent slab. In this fashion, as the adjacent slabs expand and contract, the dowels guide resultant slab movement. An exemplary dowel-type expansion joint assembly is illustrated in U.S. Pat. No. 2,500,262.
While the use of such prior expansion joints is well established, a number of very serious problems remain. In the first place, the installation of these dowel assemblies is relatively expensive and labor-intensive. In particular, it is first necessary to set the respective dowel units in laterally spaced relationship across a roadway foundation at desired joint locations, followed by pouring of concrete over the units. After the concrete is set, laterally extending slots must be cut in the concrete at the regions of dowel assemblies, so as to provide the necessary joints between respective concrete slabs. In such a procedure, it is very easy to misalign one or more of the dowel units, and moreover the subsequent cutting of expansion slots must be carefully done, lest the slots be improperly made relative to the positions of the dowel units.
In addition, experience has proved that prior dowel-type expansion joint assemblies are prone to create stress cracking in the concrete slabs, particularly at the regions directly below the dowel rod and barrel. This results from the vertical shearing loads experienced by the concrete slabs, which are only imperfectly transmitted by the dowel assemblies; as a consequence, a significant early failure rate has been encountered with these prior expansion joints.
U.S. Pat. No. 2,509,663 describes a load transfer device made up of obliquely oriented embedded rods which are twisted together at the midpoints thereof to define a joint. This design requires that the rods concurrently carry tension and compression loads, which can induce failure in the concrete roadway.
There is accordingly a real and unsatisfied need in the art for an improved expansion joint assembly which can be largely prefabricated to reduce costs, while at the same time being readily installable in the field and reducing or eliminating large shearing stresses in the surrounding concrete slabs, thereby minimizing load-induced roadway deterioration.